1. Field of the Invention
This invention relates to a stepping motor and, more particularly, relates to an improvement of a stepping motor wherein stator windings thereof can be used in a three-phase driving and a two-phase driving.
2. Description of the Prior Art
In the most of conventional hybrid type stepping motors shown in FIGS. 4 and 5 or the conventional permanent magnet type stepping motors, two-phase windings are used.
FIG. 4 shows a vertically sectional side view of a conventional hybrid type stepping motor 10.
FIG. 5 is a vertically sectional front view, taken along lines 5xe2x80x945 of FIG. 4.
In FIGS. 4 and 5, a reference numeral 1 denotes a stator housing, 2 denotes a stator core, 3-1-3-8 denote stator windings, and 4 and 4xe2x80x2 denote front and back brackets, respectively. The stator core 2 has main poles 2-1-2-8. Reference numeral 2-10 denotes pole teeth formed on the inner peripheral surface of each of the main poles 2-1-2-8.
Stator windings 3-1-3-8 are wound around the main poles 2-1-2-8, respectively. The stator core 2 and the stator windings 3-1-3-8 form a stator S.
In FIG. 4, reference numerals 5 and 5xe2x80x2 denote bearings, 6 denotes a rotor shaft, 7 and 8 denote rotary magnetic poles, 7-10 and 8-10 in FIG. 5 denote pole teeth formed on the outer peripheral surfaces of the rotor magnetic poles 7 and 8, respectively. The pole teeth 7-10 and 8-10 are deviated in the circumferential direction of said rotor magnetic poles by xc2xd pitch of the pole teeth from each other.
A rotor R is formed of said rotary shaft 6, rotary magnetic poles 7 and 8 and a permanent magnet 9 held between said two rotary magnetic poles 7 and 8.
Such rotor R is called a hybrid type rotor and forms a part of conventional two-phase hybrid type stepping motor 10.
One of the important factors showing the abilities of the stepping motor is a step angle xcex8s which is normally determined by a phase number P of stator windings or a pole tooth number Zt formed on each rotor magnetic pole and expressed by
xcex8s=180xc2x0/(Pxc2x7Zt)xe2x80x83xe2x80x83(1) 
The step angle xcex8s expressed by the formula (1) is proper to the stepping motor, and becomes small if the phase number P or the pole tooth number Zt becomes large.
The step angle xcex8s of a conventional two-phase stepping motor can be expressed by xcex8s 180xc2x0/(2xc2x7Zt) and, accordingly it is very difficult technically to manufacture a two-phase stepping motor having a very small step angle, because if the pole tooth number Zt is larger, the width of the rotor pole tooth becomes smaller.
Further, the two-phase hybrid type stepping motor makes large oscillation and noise.
Such defects can be obviated if the number of the stator main poles is increased to enhance the magnetic valance. However, no two-phase stepping motor of the main magnetic pole number other than eight or the multiple thereof can be obtained.
In the conventional stepping motor having the hybrid type rotor shown in FIGS. 4 and 5, if the number of the stator main poles is 6, the rotor tooth number becomes 6n+5 or 6n+1, where n is an integer and xe2x89xa71, so that the rotor tooth number becomes an odd number.
Accordingly, the one-phase windings are wound around the main poles separated 180xc2x0 from each other, so that if the one-phase windings are excited, the two rotor magnetic poles holding the permanent magnet therebetween are magnetized in the opposite polarities. As a result, one of the rotor magnetic poles is pulled in the upward direction, whereas the other of the rotor magnetic poles is pulled in the downward direction, and, accordingly, the rotor shaft is received a force couple normal to the axis of the rotor shaft, so that an oscillation and noise are generated.
Further, in the conventional permanent magnet type stepping motor, the main magnetic poles on which one-phase windings are wound are magnetized in the same polarity, as shown in U.S. Pat. No. 5,386,161, so that a sufficient magnetic path cannot be formed In case that the windings of one phase are excited, because no different polarities are formed on the main poles on which the one-phase windings are wound.
Accordingly, it is necessary to magnetize in the opposite polarity the main poles on which another one-phase windings are wound, and to form a magnetic path between the main poles of opposite polarities.
In this manner, a two-phase or multiple-phase excitation has to be adopted in practice.
If the phase number P of the stator windings is increased to four or five, however, the number of switches in the driving circuit is also increased.
This results in an expensive and complicated circuit.
An object of the present invention is to solve the problems mentioned above with respect to the permanent magnet type stepping motor or the hybrid type stepping motor, and to provide a three-phase permanent magnet type stepping motor of smaller step angle which can be driven by the one-phase excitation, and a two-phase permanent magnet type and hybrid type stepping motor of small oscillation and noise.
Another object of the present Invention is to provide a three-phase permanent magnet type stepping motor comprising
(1) a stator having three-phase stator windings, and 6m pieces of stator main pole arranged side by side, where m is an integer and xe2x89xa71, the stator windings of one phase being wound around every two stator main poles among the 6m pieces of the stator main pole, wherein when the stator windings of one phase are excited with a direct current, m pieces of N pole and m pieces of S pole are formed alternately on the 6m pieces of stator main pole, and
2) a rotor of a cylindrical permanent magnet magnetized in the circumferential direction so as to form Z/2 pieces of N pole and Z/2 pieces of S pole, where Z is the number of rotor poles.
The number of rotor poles is set to mxc2x7(12nxc2x12) preferably, where n is an integer and xe2x89xa71, and when n is not smaller than two, a plurality of pole teeth are formed on each of the stator main poles.
A further object of the present invention is to provide a two-phase permanent magnet type stepping motor comprising:
(1) a stator having two-phase stator windings, and 12 pieces of stator main pole arranged side by side, the stator windings of one phase being wound around every one stator main poles among the 12 pieces of the stator main pole, wherein when the stator windings of one phase are excited with a direct current, 3 pieces of N pole and 3 pieces of S pole are formed on the 12 pieces of stator main pole, and
(2) a rotor of a cylindrical permanent magnet magnetized in the circumferential direction so as to form Z/2 pieces of N pole and Z/2 pieces S pole alternately, where Z is the number of rotor poles.
The number of rotor poles is set to 24nxc2x16, where n is an integer and xe2x89xa71, and when n is not smaller than two, a plurality of pole teeth are formed on each of the stator main poles.
Yet another object of the present invention is to provide a two-phase hybrid type stepping motor comprising
(1) a stator having two-phase stator windings, and 12 pieces of stator main pole arranged side by side, the stator windings of one phase being wound around every one stator main poles among the 12 pieces of the stator main pole, wherein when the stator windings of one phase are excited with a direct current, 3 pieces of N pole and 3 pieces of S pole are formed alternately on the 12 pieces of stator main pole, and
(2) a hybrid type rotor consisting of two rotor elements of magnetic material each formed on the circumference thereof with a plurality of pole teeth and of a permanent magnet magnetized in the axial direction held between said two cylindrical rotor elements.
The number of rotor pole teeth is 12nxc2x13, where n is an integer and xe2x89xa71, and when n is not smaller than two, a plurality of pole teeth are formed on each of the stator main poles.
Yet further object of the present invention is to provide a three-phase hybrid type stepping motor comprising
(1) a stator having three-phase stator windings of U, V, and W, and 12 pieces of stator main pole arranged side by side and extending radially form an annular stator york, k pieces of pole tooth being formed on the tip end of each stator main pole, where k is an integer and xe2x89xa72, the stator windings of one phase being wound around every two stator main poles among the 12 pieces of the stator main pole, wherein when the stator windings of one phase are excited with a direct current, 2 pieces of N pole and 2 pieces of S pole are formed on the 4 pieces of stator main pole, and
(2) a hybrid type inner rotor consisting of two magnetic rotor elements each having a plurality of pole teeth on the outer peripheral surface thereof and a permanent magnet held by the two magnetic rotor elements therebetween, the one magnetic rotor element being deviated from the other in the peripheral direction by xc2xd pitch of the pole teeth, wherein the number of the pole tooth is 12kxc2x12.
In order to reduce the oscillation, it is preferable that the pitch of stator magnetic pole teeth is set to a value not larger than the pitch of rotor pole teeth.
The present invention can be applied on the outer rotor type stepping motor. In this case, the permanent magnet may be provided on the stator. In case of the windings of star connection, the winding ends of the windings of U, V and W phases are connected together and the winding direction of the windings of one phase is reversed to that of the remaining phases.
Still another object of the present invention is to provide a three-phase annular winding cascade craw-pole type stepping motor and a driving method thereof, the stepping motor comprising
(1) a rotor consisting of a cylindrical magnet magnetized in the circumferential direction so as to form M pieces of N pole and M pieces S pole alternately, where M is an integer and xe2x89xa72, and
(2) a stator having annular three stator units arranged in the axial direction of the rotor concentrically with the rotor axis, each of said stator unit consisting of two opposite stator cores having craw poles extending axially on the Inner peripheral surface thereof, and of one of three stator windings of U, V and W phases held between said two stator cores, said windings of U, V and W phases being arranged in this order in the axial direction, said craw poles being separated by 180xc2x0/M from one another and magnetized by said stator winding in opposite polarities alternately, said three stator windings being connected to form a star or delta connection, adjacent craw poles magnetized by the stator windings of U phase and V phase are deviated by 60xc2x0/M from each other in the circumferential direction, and adjacent craw poles magnetized by the stator windings of V phase and W phase are deviated by 60xc2x0/M from each other in the circumferential direction, said annular stator windings being excited so that a magnetic flux generated by the annular stator windings of one phase in the axial direction becomes always opposite to that by annular stator windings of the other phase, in case of two phase exciting driving.
Still another object of the present invention is to provide a three-phase annular winding cascade claw-type stepping motor and a driving method thereof, the stepping motor comprising:
a rotor consisting of a cylindrical magnet magnetized in the circumferential direction so as to form M pieces of N pole and M pieces S pole alternately, where M is an integer and xe2x89xa72, and
a stator having annular three stator elements arranged in the axial direction of the rotor concentrically with the rotor axis, each stator element consisting of two opposite stator cores having claw poles extending axially from the inner peripheral surface thereof, and of three stator windings of U, V and W phases held between the two stator cores, the windings of U, V and W phases being arranged in this order in the axial direction, the claw poles being separated by 180xc2x0 from one another and magnetized by said stator windings in opposite polarities alternately, the three stator windings being connected to form a star or delta connection,
adjacent claw poles magnetized by the stator windings of U phase and V phase are deviated by 120xc2x0/M from each other in the circumferential direction, and adjacent claw poles magnetized by the stator windings of V phase and W phase are deviated by 120xc2x0/M from each other in the circumferential direction, the annular stator windings being excited so that a magnetic flux generated by annular stator windings of one phase in the axial direction becomes always the same to that generated by the other annular stator windings adjacent to the annular stator windings of the one phase, but a magnetic flux generated by the annular stator windings in the axial direction becomes always opposite to that generated by the annular stator windings which is not adjacent to the annular stator windings of the one phase, in case of two phase exciting driving.
These and other objects and features of the present Invention will become apparent from the following description in conjunction with the attached drawings.